Torsion of Thin Walled Sections Questions and Answers

Answer: C

The table sorts the sections by how they behave in torsion. Open sections dominate the trouble column, closed sections the efficiency column, and the circular shaft sits alone as the case the elementary theory describes exactly.

Answer: D

Divergence and control reversal both depend on how readily the wing twists, so torsional rigidity is an aeroelastic requirement in addition to a strength one. That double role is why the closed torsion box is defended so firmly against cut-outs and thinning.

Answer: A

Any opening large enough to break the continuity of the shear flow locally converts that bay towards open-section behaviour. Undercarriage bays and access panels are therefore ringed with heavy edge members and, where possible, closed by structural doors.

Answer: B

Latching the door into the surrounding structure lets shear pass through it, restoring most of the torsional continuity the cut-out removed. The alternative is to carry the load entirely in the frame around the opening, which is considerably heavier.

Answer: C

Correct answer: 3.27e-3 m^4

Bredt’s formula gives \[ J = \frac{4A^2t}{s} = \frac{4(1.2)^2(0.0025)}{4.4} \] \[ = \frac{0.0144}{4.4} = 3.27 \times 10^{-3}\ \mathrm{m^4}. \] The enclosed area appears squared and the thickness only to the first power, which is why a wing box gains far more torsional stiffness from depth and chord than from skin gauge.

Answer: D

Both are true and the second explains the first. The load must divert round the opening, and without stiff edge members the local behaviour tends towards that of an open section, with a collapse in torsional stiffness across that bay.

Answer: A

Correct answer: 1, 2 and 3

All three are correct and together they describe how cut-outs are handled. An opening breaks the circulating shear flow, so the load must divert around it; heavy edge members and corner fittings are provided to carry that diverted load; and a door that latches structurally at several points can restore a large part of the shear path, which is why undercarriage and cargo doors are designed to do so.

Answer: B

Correct answer: Making the opening as large as possible to reduce weight

This inverts the trade. A larger opening interrupts more of the shear circuit and demands heavier edge members and corner fittings, so it costs weight rather than saving it. The other three are the standard measures: keep the opening no larger than the function requires, ring it with heavy edge members, and make the door itself carry load.

Answer: C

The Bredt-Batho mechanism outperforms St Venant torsion by two or three orders of magnitude, and wing torsional stiffness sets the divergence and reversal speeds as well as the stress. Everything about the box's layout follows from protecting that closed cell.

Answer: D

Torsion analysis produces the angle of twist and the shear stress for a given torque and section, and identifies which theory applies to each shape. Both outputs feed into strength checks and into the aeroelastic clearance of the wing.